(HealthDay News) -- Even a few extra pounds and just a little inactivity increased the risk of heart failure in a major study of American doctors.

"What this study shows is that even overweight men who are not obese have an increase in heart failure risk," said Dr. Satish Kenchaiah, lead author of a report on the finding in the Dec. 23 issue of Circulation.

As for exercise, "even a little amount of physical activity appears to decrease the risk of heart failure," said Kenchaiah, who did the research as a epidemiologist at Brigham and Women's Hospital in Boston and is now at the U.S. National Heart, Lung, and Blood Institute.

The study has followed more than 21,000 doctors for two decades, measuring among other factors the influence of overweight and physical activity on development of heart failure, the progressive loss of ability to pump blood, which is often a prelude to major coronary events.

Outright obesity, defined as a body-mass index of 30 or over, has long been known as a risk factor for heart failure. The new report concentrated on men who were borderline overweight, with a body-mass index of 25 to 29.9.

About 5 percent of the doctors were obese, and 40 percent were overweight, when the study began. Adjusting for other risk factors such as high blood pressure and high cholesterol, the study found a 49 percent increased incidence of heart failure in overweight men compared to those with a body-mass index of 25 or less. Incidence of heart failure was 180 percent for the obese men compared to the leaner ones.

It was the same story for physical activity. "Men who engaged in physical activity anywhere from one to three times a month had an 18 percent reduction in heart failure risk," Kenchaiah said. "For those who were active five to seven times a week, the reduction was 36 percent. The more you exercise, the more reduction you achieve."

The association of even minimal physical activity with reduced risk could be explained as an indicator of good habits in general, he said. "It is possible that they have a healthier lifestyle in general," Kenchaiah said.

The study found that doctors who rarely or never exercised were older, smoked cigarettes more often, and were more likely to have high blood pressure or diabetes.

"This new report reinforces what we've said in the past," said Dr. Gerald Fletcher, a preventive cardiologist at the Mayo Clinic in Jacksonville, Fla. "Not being obese but being overweight is definitely a risk factor for heart failure."

While Fletcher said he would have liked a more definitive indicator of physical activity -- the report described it as simply breaking a sweat -- he said the study showed again that "vigorous exercise makes the difference. The more you do, the better it is for you."

Two-thirds of Americans have excess body weight, and only about 30 percent exercise regularly, Kenchaiah said. About 660,000 new cases of heart failure are diagnosed each year in the United States, he said, and 80 percent of the men and 75 percent of the women aged 65 and older who are diagnosed with heart failure die within eight years.